An analysis of more than 7 million speeches by lawmakers suggests that politicians use simpler language on high-temperature days, which researchers say may point to a potential effect of a warming climate on cognition.

The study, published in iScience, looked at 7.4 million speeches given by over 28,500 legislators in eight countries in an attempt to learn whether extreme temperatures might affect cognitive performance — even indoors. Extreme heat and cold are expected to become more frequent and intense as climate change progresses, with extreme temperatures linked to a variety of health problems.

The researchers analyzed the texts of speeches given in D.C.; London; Vienna; Amsterdam; Wellington, New Zealand; Copenhagen; Madrid; Bonn, Germany; and Berlin between 1950 and 2019, linking temperature data from the day of the speech to the language used by legislators.

The analysis showed that language proficiency among politicians decreased on high-temperature days, but not on cold days, with heat decreasing the language complexity score equivalent to “approximately a half month of lower educational attainment.” Speeches given on hot days had 3.3 percent shorter word lengths, though sentence lengths stayed the same.

When the researchers analyzed a subset of the data from Germany, they found that for legislators over age 57, the effects of heat began at 69.8 to 75.2 degrees Fahrenheit. Language complexity during hot periods differed between men and women but not to a statistical significance. The effects carried over to indoor speeches, the researchers said, theorizing that lawmakers’ brief exposure to outdoor heat on their way to give speeches could have an impact and noting that “extreme temperatures can also disrupt sleep.”

“The simplification of political discourse has mixed implications; while simpler language can enhance public understanding and engagement, it might also signal reduced cognitive performance due to heat,” Tobias Widmann, an assistant professor of political science at Aarhus University in Denmark and a co-author of the study, said in a news release. “This could have negative consequences for the productivity of parliament members, affecting legislative decision-making, citizen representation and budget planning.”

The study did not test specific mechanisms behind drops in language complexity, and the researchers note that many political speeches are written well before they are given. They recommend that future research include more advanced measures of language and more demographic data on the speakers. Nevertheless, they write, extreme temperatures could “have far-reaching negative implications for society as a whole.”